The interaction energy of three neutral molecules that form a nanocluster is studied. It is assumed that one molecule (M$_0$ ) has a dipole moment, while the other two (M$_1$ and M$_2$ ) are nonpolar. The molecule interaction energy in such a nanocluster is determined by the sum of dispersion interaction energies of each pair of molecules and the sum of inductive energies of the molecules. Analytical expressions for these energies as functions of the distance between the centers of mass of the molecules have been obtained. A method for the determination of damping functions which takes the contribution of repulsive forces into account has been developed. Analytical expressions for the molecule interaction energies for a two-molecule cluster in an external field of the third molecule have been obtained. A nanocluster consisting of a molecule of polar isomer pentene C$_5$H$_{10}$ and a nonpolar molecule of polycyclic aromatic hydrocarbon pyrene C$_{16}$H$_{10}$ in the external electrostatic field of another pyrene molecule is considered. The calculation showed that the interaction energy of the two-molecule nanocluster increases by a factor of 1.5 if this cluster is in the field of the induced dipole moment of an external pyrene molecule.
36.40.-c Atomic and molecular clusters
$^1$Lomonosov Moscow State University, Skobeltzin Institute of Nuclear Physics. 119992, Moscow, Russia.
$^1$Philipps-University, D-06421 Marburg, Germany.
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